Cost Effective Implementation of Fixed Point Adders for LUT based FPGAs using Technology Dependent Optimizations

Abstract

Modern day field programmable gate arrays(FPGAs) have very huge and versatile logic resources resulting inthe migration of their application domain from prototypedesigning to low and medium volume production designing.Unfortunately most of the work pertaining to FPGAimplementations does not focus on the technology dependentoptimizations that can implement a desired functionality withreduced cost. In this paper we consider the mapping of simpleripple carry fixed-point adders (RCA) on look-up table (LUT)based FPGAs. The objective is to transform the given RCABoolean network into an optimized circuit netlist that canimplement the desired functionality with minimum cost. Weparticularly focus on 6-input LUTs that are inherent in all themodern day FPGAs. Technology dependent optimizations arecarried out to utilize this FPGA primitive efficiently and theresult is compared against various adder designs. Theimplementation targets the XC5VLX30-3FF324 device fromXilinx Virtex-5 FPGA family. The cost of the circuit is expressedin terms of the resources utilized, critical path delay and theamount of on-chip power dissipated. Our implementation resultsshow a reduction in resources usage by at least 50%; increase inspeed by at least 10% and reduction in dynamic powerdissipation by at least 30%. All this is achieved without anytechnology independent (architectural) modification.